At present, as a magnet for motors requiring a power torque which are used in various applications including not only hybrid cars and electric cars but also familiar domestic appliances such as air conditioners and washing machines, there have been used Nd—Fe—B-based magnetic particles and a molded product thereof. However, there is almost present a theoretical limitation with respect to use of the Nd—Fe—B-based magnetic material as a magnet.
In addition, supply of rare earth elements as the raw materials largely depends upon import from china in view of low costs of the raw materials and a low content of isotope elements in the raw materials, i.e., there is present the large problem of so-called “china risk”. For this reason, Fe—N-based compounds such as Fe16N2 containing no rare earth elements have been noticed.
Among the Fe—N-based compounds, α″-Fe16N2 is known as a metastable compound that is crystallized when subjecting a martensite or a ferrite comprising nitrogen in the form of a solid solution therewith to annealing for a long period of time. The α″-Fe16N2 has a “bct” crystal structure, and therefore it is expected that the α″-Fe16N2 provides a giant magnetic substance having a large saturation magnetization. However, as understood from the “metastable compound”, there have been reported only very few successful cases where the compounds could be chemically synthesized in the form of isolated particles.
Hitherto, in order to obtain an α″-Fe16N2 single phase, various methods such as a vapor deposition method, an MBE method (molecular beam epitaxy method), an ion implantation method, a sputtering method and an ammonia nitridation method have been attempted. However, production of more stabilized γ′-Fe4N or ε-Fe2-3N is accompanied with an eutectic crystal of martensite (α′-Fe)-like metal or ferrite (α-Fe)-like metal, which tends to cause difficulty in producing the α″-Fe16N2 single phase compound in an isolated state. In some cases, it has been reported that the α″-Fe16N2 single phase compound is produced in the form of a thin film. However, the α″-Fe16N2 single phase compound in the form of such a thin film may be applied to magnetic materials only in a limited range, and tends to be unsuitable for use in still more extensive application fields.
The following known techniques concerning the α″-Fe16N2 have been proposed.